The general goal of this study is the experimental and clinical applications of DNA damage assay in individual cells based on the staining of cells with anti-DNA monoclonal antibody. Flow cytometric measurements of DNA damage in the cells treated with alkylating agents was shown to evaluate drug resistance in heterogeneous cell populations, to analyze DNA repair and to select therapeutically useful DNA repair inhibitors. DNA repair and its inhibition by chemotherapeutic agents will be studied to develop screening system for efficient repair inhibitors and to develop rational basis for combination chemotherapy based on DNA repair inhibition. The effects of drugs of different classes and their combinations of the repair of DNA damage induced by alkylating agents in cell lines representing major tumor localizations will be studied. The goal of clinical applications is to develop chemosensitivity tests for ovarian carcinomas, multiple myeloma, chronic myeloid leukemia and chronic lymphoid leukemia. Solid tumors will be treated in vitro with alkylating agents, disaggregated and DNA damage will be measured in aneuploid tumors cells. Cells isolated from blood and bone marrow will be treated with alkylating agents and DNA damage will be measured on a flow-cytometer. The intensity of DNA damage induced by drugs in vitro will be compared with the response of patients to chemotherapy with alkylating agents. The effect of DNA repair inhibitors on DNA damage induced by alkylating agents in ovarian tumors in vitro will be studied in order to determine the sensitivity of individual tumors to DNA repair inhibition. The rate of DNA repair in leukemic cells will be evaluated by decrease of DNA immunoreactivity during post-incubation in drug-free medium. Rate of repair will be correlated with the development of resistance. The role of cell interaction in the development of drug resistance will be studied in cell culture and xenografts of human tumors. Screening system for drugs which eliminate resistance based on interaction of cell subsets with different mechanisms of resistance will be developed.